Bread-Bakers v111.n022.4

I've been baking this bread for some time and recently have 
experienced some trouble.  Initially I used only Bread or All Purpose 
flour. Lately I have changed to include 25% rye flour. The bread 
turns out more dense. It does not grow as much during the 18 hours 
rise. The bread also does not gain much in size during the baking 
process. Any suggestions on what I may be doing wrong to cause this?

Gene
Tallahassee, FL